Method of producing cube-on-corner oriented electrical steel sheet



United States Patent 3,540,948 METHOD OF PRODUCING CUBE-ON-CORNER ORIENTED ELECTRICAL STEEL SI-[EET James G. Benford, Monroeville Borough, and Edward B.

Stanley, Washington Township, Westmoreland County,

Pa., assignors to United States Steel Corporation, a

corporation of Delaware No Drawing. Filed Dec. 18, 1967, Ser. No. 691,130

Int. Cl. H01f N16 US. Cl. 148-111 3 Claims ABSTRACT OF THE DISCLOSURE An electrical sheet steel having a cube-on-corner or (111) [IE] preferred orientation produced by annealing at a temperature of at least about 2000 F. in the presence of a selenide or telluride.

This invention relates to a method of producing a new preferentially oriented electrical steel sheet and to a new electrical steel article. More particularly, the invention relates to a method for producing electrical steel sheet having a cube-on-corner or (111)[1l] preferred orientation.

Preferred orientation in accordance with the invention, i.e. cube-on-corner orientation, exhibits essentially isotropic magnetic properties in all directions in the plane of the sheet. This orientation is of particular advantage for thin, i.e. less than 0.011 inch thick, electrical steel sheets because of the development of relatively anisotropic preferred orientations during the usual methods of processing thin nonoriented electrical sheets. Moreover, material having a cube-on-corner preferred orientation is especially desirable as core material in rotating electrical equipment such as motors or generators because of the almost equal magnetic properties in all directions in the plane of the electrical sheet. By practicing the invention, an essentially magnetically isotropic material is produced by an easily practiced method.

In accordance with the invention, electrical steel sheet having a cube-on-corner preferred orientation as described above is obtained by annealing silicon steel in a selenideor telluride-containing atmosphere at a temperature of at least 2000 F. This invention is particularly applicable to silicon steels containing nominally 3% silicon and improves upon the product produced by the conventional method of processing which involves annealing cold reduced conventionally produced electrical steel sheet having a cube-on-edge (110) [001] orientation. In practicing the invention, annealing is performed in the presence of a selenide or telluride and cube-on-corner (lll)[1l] orientation develops in the steel. Conventionally produced oriented electrical steel sheets are manufactured by a double cold reduction followed by recrystallization annealing and a final high temperature anneal in which the cube-on-edge orientation is developed. We have found that if such conventionally produced oriented steel is further cold reduced and then annealed, the presence of a compound of selenium or tellurium, i.e. selenide or telluride, in the annealing atmosphere will cause the development of the desirable cube-on-corner orientation. If the selenides or tellurides are not present in the atmosphere, a cube-on-face orientation (100) [001] rather Patented Nov. 17, 1970 ICCv than a cube-on-corner orientation will be developed. Furthermore, it has been found that metal vapor, e.g. selenium vapor, in the annealing atmosphere does not develop the preferred crystallographic orientation. A compound, such as hydrogen selenide, is necessary to develop the cube-on-corner orientation.

As an example of the practice of the invention, an ll-mil thick commercial oriented silicon steel containing 2.94% silicon with cube-on-edge orientation was lightly pickled and cold reduced 55% to a S-mil thick sheet. The steel was then annealed in a charge containing steels bearing 0.02 to 0.05% selenium and constituting 20 to 50% of the surface area of the materials in the charge. The steel was heated in about 1 hour to 1400 F. and then at 60 F./hour to 2200 R, where it was held for 4 hours to encourage secondary recrystallization, and then furnace cooled. The desired annealing atmosphere was created by flowing dry hydrogen at about 4 cubic feet/hour in a chamber having a volume of 0.05 cubic feet. The extent of the cube-on-corner orientation development was determined by X-ray diffraction through analysis of Laue back-reflection patterns of many grains of each sample. The orientation development by treating in the seleniumor tellurium-containing atmosphere is usually in excess of and very often in excess of The properties of electrical steel made in accordance with the invention are superior to conventional materials. This can be seen by comparing properties of steels of different preferred crystallographic orientation. The results of a series of tests in this regard are reported in Table I which reports core loss for commercial steel sheet and cube-on-corner oriented steel of identical composition treated in accordance with the invention.

TABLE I Steel: Core loss, watts/pound/ 10 kg./ 60 Commercial /2 transverse, /2 longitudinal 0.67 Commercial (all longitudinal 0.56 Cube-on-corner (longitudinal 0.44

1 Rolling direction.

In a magnetic torque test, cube-on-corner material in accordance with the invention exhibited a maximum torque 'of about 7000 dyne-cm./cm. which is an indication of the very low magnetic anisotropy of this orientation. The steel with the cube-on-corner orientation exhibited a core loss of 0.44 watt/lb. at 10 kg. and 60 cycles. This loss compares very favorably With the value of 0.56 watt/pound at 10 kg. and 60 cycles observed with a commercial 5 mil thick nonoriented silicon steel measured in the rolling direction only.

The core loss data in the rolling direction is available from published sources in the ranges described. It is apparent from the data in Table I that the core loss of the same commercial 5 mil thick steel compares even less favorably in a test involving the average of transverse and rolling directions. In this case, the core loss at 60 cycles obtained was 0.67 'Watt/ lb. at 10 kg.

In addition to the above, the cube-on-corner steel possesses superior AC permeability from 500 up to 6000 gausses when compared with data for 5 mil thick commercial electrical nonoriented steel sheets. The results of a series of tests of this property are described in Table II. As can be seen, at 500 and 6000 gausses the cube-on-corner orientation in accordance with the invention exhibited permeabilities of 2900 and 12,000 respectively, compared to permeabilities of 2100 and 9100 for commercial electrical steel not having the orientation in accordance with the invention. It was observed that the cube-on-corner material exhibited a maximum permeability of about 13,000 at 8000 gausses. By comparison, the commercially produced steel exhibited a maximum AC permeability of less than 11,000.

1 Rolling directlon.

The presence of selenide or telluride in the annealing atmosphere is essential to the production of the cube-oncorner orientation by secondary recrystallization. While it is not known for certain, it is believed that the preferred orientation occurs by a surface energy phenomenon at least in its early stages and that grain boundary energy dominates late in the development. However, metal vapor does not appear to yield the same results and some compound of selenium or tellurium is required. The preferred selenium or tellurium source is a compound with hydrogen which may be formed in situ within the annealing chamber or introduced into the annealing atmosphere before entering the annealing chamber.

Hydrogen selenide may be developed either by reaction of hydrogen gas with selenium contained in another steel in the same annealing chamber or by any other chemical reaction. For example, the hydrogen selenide could be generated by passage of hydrogen over selenium metal at an appropriate temperature at some remote location. Hydrogen selenide could then be swept with the hydrogen into the annealing chamber.

The following example shows that the selenide or telluride is the critical component in the atmosphere and not selenium metal vapor. Samples from the same lot of steel were annealed in hydrogen and in helium. In both anneals the same amounts of selenium-bearing steel were included with the subject steel. The distinction is important inasmuch as helium, unlike hydrogen, will not react with selenium to form a selenide. In both anneals, selenium metal vapor was present. Steels heated in hydrogen developed extensive amounts of cube-on-corner texture,

whereas those treated in a helium atmosphere developed little or no cube-on-corner texture. It can therefore be concluded that the selenide, in this case hydrogen selenide, rather than selenium metal vapor is critical to the development of cube-on-corner texture. Although other selenides exist that would work, few are gaseous in the desired temperature range and since none would be as convenient to use as hydrogen selenide, the latter is preferred.

It is apparent from the above that various changes and modifications may be made without departing from the invention.

Accordingly, the scope of the invention should be limited only by the appended claims wherein what is claimed is:

1. A method of producing electrical sheet steel of improved isotropic magnetic properties the steps comprising cold rolling a silicon steel to a thickness of no more than about 0.011 inch, annealing the cold rolled silicon steel at a temperature of at least 2000 F. in an atmosphere containing at least one compound from the group consisting of hydrogen selenide and hydrogen telluride to produce a cube-on-corncr (111) [112] preferred crystallographic orientation.

2. A method according to claim 1 in which the silicon steel, prior to cold rolling, is a conventional grain oriented silicon steel sheet having a cube-on-edge [001] prefered orientation.

3. A method according to claim 1 in which the compound from the group hydrogen selenide and hydrogen telluride is produced in situ during annealing.

References Cited UNITED STATES PATENTS 3,130,093 4/1964 Kohler 148-413 X 3,130,095 4/1964 Kohler et al. 1481 13 3,392,063 7/1968 Kohler 148113 X FOREIGN PATENTS 229,565 1/1964 Netherlands. 652,133 11/1962 Canada.

L. DEWAYNE RUTLEDG-E, Primary Examiner G. K. WHITE, Assistant Examiner US. Cl. X.R. 

